1. Field of the Invention
The present invention relates to a communication method and system having at least one communication network to which a plurality of subscribers are attachable.
2. Description of the Prior Art
Communication systems for mobile communication such as GSM (Global System for Mobile Telecommunications), GPRS (General Packet Radio Service), or UMTS (Universal Mobile Telecommunications System) networks usually comprise one or more home location registers (HLRs) for permanent storage of subscriber information such as IMSI (International Mobile Subscriber Identity), one or more VLRs (Visitor Location Registers) providing access to the subscriber equipment, one or more MSCs (Mobile Switching Centers) for transmitting data to the user equipments, and the like. When a connection is to be connected to a subscriber e.g. from an external network, the home location register will normally be accessed for receiving information necessary for properly routing of the connection.
One of several possible procedures to be performed between a user equipment such as a mobile station (MS) and the network for connecting an external network is a so-called “PDP context activation”, wherein PDP stands for packet data protocol. Such a PDP context activation may be performed in particular in a packet switched network such as a GPRS network wherein several information elements such as requested or negotiated QoS (Quality of Service) and/or PDP address are transmitted between the user equipment (MS) and a support node handling the communication with the user equipment. Such a “PDP context activation” procedure is a standardized process and is e.g. described in the publication ETSI (European Telecommunications Standards Institute) EN 301 344 V6.3.2 (1999-07), pages 59 ff. This process is therefore not be explained here in further detail. (For more detailed information, it is referred to the above mentioned document.) The “PDP context activation” procedure may be initiated by a mobile station intending to attach to the network after switch-on, for instance, or may be requested by the network and is then called “network-requested PDP context activation” (NRCA) procedure. See for instance EN 301 344, section 9.2.2.2.
Such a network-requested PDP context activation procedure allows for example a GGSN (Gateway GPRS support node) to initiate the activation of a PDP context. When receiving a PDP (Packet Data Protocol) PDU (Protocol Data Unit), the GGSN may check if a PDP context has already been established for that PDP address. If no PDP context has previously been established, the GGSN may try to deliver the PDP PDU by initiating a network-requested PDP context activation procedure. The GGSN may send a message (containing e.g. IMSI, International Mobile Subscriber Identification) to the home location register HLR requesting routing information for GPRS. When the HLR determines that the request can be served, it returns a message to the GGSN indicating routing information.
When the HLR determines that the request cannot be served (e.g. the IMSI is unknown in HLR), the HLR will send back a negative response indicating the reason for non-service.
Furthermore, the gateway node may store an information “Mobile Station Not Reachable for GPRS” (MNRG flag) indicating whether or not a user equipment such as a mobile station can be reached.
In addition, the gateway node is usually stores the address of the support node with which the gateway established the last connection for transmitting data to and/or from a user equipment (e.g. last PDP context). The GGSN also should store the mapping between PDP address (ie IP address) and IMSI. The gateway hence requires a large storage capacity for storing the information which will be retained even for presently not active user equipments.